This invention relates to the manufacture of solid electrolytic capacitors and more particularly to making solid electrolytic tantalum capacitors by forming a porous tantalum pellet on a substrate having at least one face made of tantalum, wherein the tantalum face serves as the anode connection.
The majority of solid tantalum capacitors are made today by compressing a free-flowing tantalum powder, either with or without a binder, into a mold, removing from the mold, sintering, forming a dielectric oxide, covering with a solid electrolyte and forming a counterelectrode.
For those uses requiring high component packing densities especially in planar mounting and hybrid integrated circuit systems, there have been proposed several varieties of solid tantalum capacitor structures employing a tantalum substrate carrier. In several cases, the tantalum substrate has cavities or cups formed therein, in which tantalum powder is dispersed and sintered. In another arrangement, a flat tantalum substrate is overlaid by a tantalum template wherein the powder is confined. The geometry of the above mentioned substrates or templates narrowly determines and limits the geometry of the porous tantalum pads thus produced. The template system is particularly limiting since the thickness of the template determines closely the height of the tantalum powder pads and must either be carefully removed to avoid destroying pads or must be carried through the sintering process. The previous systems of powder on substrate require a special commitment to tooling for each size of capacitor to be produced, not unlike the more conventional molded pellet system. In addition, the methods of the prior art tend to produce a sintered tantalum body having a smooth surface. Thus the introduction for example of a solution of manganous salts into the porous body is achieved by special means that must overcome the tendency of the salt solution to run off of the smooth surface.
These previous methods are suitable for making a number of solid tantalum capacitors on the same substrate. However they are limited by the necessary tooling with respect to the minimum capacitor size and spacing between capacitors. It is desirable to achieve smaller capacitors having high capacity-voltage capability and closer spacing, both for the advantages of further miniaturization and for the economy of production.
It is therefore an object of the present invention to provide highly miniaturized solid tantalum capacitors.
It is a further object of this invention to provide multiple solid tantalum capacitors having a high packing density.
It is a further object of this invention to provide a process for manufacturing solid tantalum capacitors requiring only low cost and readily acquired tooling, which method will reduce the cost of manufacturing.
It is a further object of this invention to provide solid tantalum capacitors being capable of direct connection or connection by use of leads and otherwise potentially capable of meeting a great variety of requirements for packaging and mounting.
These and other objects will become apparent in the following description.